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Abstract

Effects of GSM 900MHz signals (EMF) typical for a handheld mobile phone on the cerebral blood circulation were investigated using near-infrared spectrophotometry (NIRS) in a three armed (12W/kg, 1.2W/kg, sham), double blind, randomized crossover trial in 16 healthy volunteers. During exposure we observed borderline significant short term responses of oxyhemoglobin and deoxyhemoglobin concentration, which correspond to a decrease of cerebral blood flow and volume and were smaller than regular physiological changes. Due to the relatively high number of statistical tests, these responses may be spurious and require further studies. There was no detectable dose-response relation or long term response within 20min. The detection limit was a fraction of the regular physiological changes elicited by functional activation. Compared to previous studies using PET, NIRS provides a much higher time resolution, which allowed investigating the short term effects efficiently, noninvasively, without the use of radioactive tracers and with high sensitivity.

The short term changes in deoxyhemoglobin (HHb) concentration during three types of exposure: 12W/kg, 1.2W/kg and sham. Data were obtained from the left side of the head, which was towards the antenna. The symbols indicate the mean and the whiskers the 95% confidence interval (CI 95%). The results are displayed separately for the three different interoptode distances of 1.25cm (left), 2.5cm (middle) and 3.75cm (right). The depth of the interrogated tissue depends on the interoptode distance, i.e. the short distance of 1.25 mostly detects changes in the superficial layer of the head (skin and skull), while the longest distance also contains information about the brain. The data are displayed for the different periods of measurement: the 20s of exposure (Exp), the first 20s after exposure (Post1) and the second 20s after exposure (Post2). At 1.25cm the difference between HHb during exposure with 12W/kg and 1.2W/kg is statistically significant (p=0.011, Wilcoxon). Furthermore, the CI 95% between sham and 1.2W/kg was significantly different at 2.5cm distance for the Exp (p=0.001) and Post1 (p=0.015) periods. Otherwise there were no significant differences between the three types of exposure.

The short term changes in oxyhemoglobin (O2Hb) concentration during three types of exposure: 12W/kg, 1.2W/kg and sham. Data were obtained from the left side of the head, which was towards the antenna. This figure is analogous to Fig. 3. At 2.5cm the difference between O2Hb during exposure with 12W/kg and sham is statistically significant (p=0.016, Wilcoxon). Otherwise there were no significant differences between the three types of exposure.

The short term changes in deoxyhemoglobin (HHb) concentration during three types of exposure: 12W/kg, 1.2W/kg and sham. Data were obtained from the right side of the head, which was on the opposite side of the antenna. This figure is analogous to Fig. 3. The CI 95% between sham and 12W/kg was significantly different at 3.75cm distance for the Post1 (p=0.011) period. There were no other significant differences between the three types of exposure.

The short term changes in oxyhemoglobin (O2Hb) concentration during three types of exposure: 12W/kg, 1.2W/kg and sham. Data were obtained from the right side of the head, which was on the opposite side of the antenna. This figure is analogous to Fig. 3. At 2.5cm the difference between O2Hb during exposure with 12W/kg and 1.2W/kg is statistically significant (p=0.009, Wilcoxon) and analysis of variance showed a significant difference between the three types of exposure during this period (p=0.009). Otherwise there were no significant differences between the three types of exposure.

The long term changes over 20min in oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb) concentration during three types of exposure: 12W/kg, 1.2W/kg and sham. The results are displayed separately for the three different interoptode distances of 1.25cm (left), 2.5cm (middle) and 3.75cm (right). The data from the left side was close to the antenna while the right side was further away form the antenna. The whiskers correspond to the CI 95%. There were no significant differences between the three exposure types.